Microwave Transmission

In the electromagnetic spectrum, waves within the frequencies 1GHz to 300GHz are called microwaves.

Features of Microwaves

• Microwaves travel in straight lines, and so the transmitter and receiver stations should be accurately aligned to each other.

• Microwave propagation is line – of – sight propagation. So, towers hoisting the stations should be placed so that the curvature of the earth or any other obstacle does not interfere with the communication.

• Since it is unidirectional, it allows multiple receivers in a row to receive the signals without interference.

• Microwaves do not pass through buildings. So, indoor receivers cannot be used effectively.

• Microwaves are often refracted by the atmospheric layers. The refracted rays take longer time to reach the destination than the direct rays. This causes out of phase transmission, called multipath fading.

• Microwaves need unidirectional antennas to send out signals. Two types of antennas are needed −

  • Parabolic Dish Antenna − It is used by the receiving station. It is parabolic in shape, which concentrates all energy to a small beam thus achieving a strong signal with high SNR.

  • Horn Antenna − It has a stem with a curved head. In sending stations, outgoing waves from the stem are broadcast by the curved head as a series of parallel beams. In the receiving station, the rays are collected by the curved head and deflected in the stem.

• Applications

  • Long distance telephone communication
  • Cellular phones
  • Television networks
  • Satellites
  • Wireless LANs